Wind energy has not been utilized extensively by industry in the United States because of economics. Wind energy seems to be most promising in the generation of electricity at specific sites where wind velocities are high and reasonably steady. However, these sites tend to be remote from most industrial locations. Noise generation, safety considerations and television interference also tend to discourage the use of wind devices in congested areas.
To date, wind conversion devices have been proposed and built in a very wide variety of types. The most common type is the horizontal-axis head-on type, typical of conventional farm windmills. The axis of rotation is parallel to the direction of the wind stream. Where the wind direction is variable, the device must be turned into the wind either by a tail vane or by a servo device or the like. The rotational speed of the device can be controlled by feathering the blades or by flap devices or by varying the load.
Another form of wind conversion device is the vertical-axis wind turbine (VAWT). Examples of such devices are the Savonius or Darrieus types. In such devices, wind direction is not important, which is a tremendous advantage. Furthermore, the system is simple, and no stresses are created by yawing or turning into the wind as occurs on horizontal-axis devices. A VAWT is lighter in weight, requires only a short tower base and can have the generator near the ground as compared to horizontal-axis devices.
While successful, even the VAWT system can be improved by improving the efficiency thereof. One area of inefficiency is the turbulence created adjacent to the blades as wind moves therepast. This turbulence may affect the operation of other blades and the overall system efficiency. The turbulence is often created because the blades of the device are not oriented properly to take maximum advantage of the wind, or because of the characteristics of the fluid flow associated with the blades.
Therefore, there is a need for a wind conversion device that takes maximum advantage of the flow of air past the device.